1. Field of the Invention
The present invention relates to an exposure device, and more particularly, to an exposure device using electro-luminescence (EL) elements as a light source.
2. Description of the Related Art
An organic electric field light emitting element that employs a fluorescent organic substance as a material for a light emitting layer is referred to as an xe2x80x98organic EL elementxe2x80x99. Since the organic EL element has such advantages that manufacturing thereof is more facilitated than other light emitting elements and a thin and light weight light emitting element can be formed, the organic EL element has conventionally been studied and developed as a thin type display element. In recent years, a high performance organic EL element, which is comparable with a light emitting diode (LED) in terms of light emitting luminance, light emitting efficiently, durability, and the like, has been developed. Therefore, application has been studied of an organic EL element to an exposure head for exposing a photosensitive material such as a silver halide photosensitive material. For example, Japanese Patent Application Laid-Open (JP-A) No. 7-22649 discloses a light exposing device having an optical recording unit using the organic EL element.
Typically, an organic EL element is structured such that an organic compound layer having a light emitting layer is provided on a transparent substrate, and a pair of electrode layers (including a cathode layer and an anode layer) for interposing the organic compound layer therebetween is layered. The emitted light is outputted from the transparent substrate side. However, since the emitted light is a diffusing light source and reflected from the transparent substrate, light outputting efficiency becomes low, and a sufficient exposure amount can be obtained.
Conversely, Japanese Patent Application Laid-Open (JP-A) No. 10-172756 discloses an organic EL light emitting device in which a microlens is placed on the organic EL element between a light emitting layer, and a light outputting surface of the transparent substrate so as to correspond to each other 1 to 1 to thereby improve the light outputting efficiency and increase light emitting luminance in the direction of optical axis. Further, Japanese Patent Application Laid-Open (JP-A) No. 11-354271 discloses a photosensitive material recording device in which an organic EL element array is formed on a substrate having a microlens, whereby availability of the emitted light amount has improved.
However, when the aperture area of the microlens has the same dimension as that of a light emitting portion of the organic EL element, a problem is caused in that the light emitted from the light emitting portion cannot be converged sufficiently, whereby the exposure amount of the light becomes insufficient. Further, a problem has also arisen in that, since the organic EL element is a diffusing light source, crosstalk may occur when the area of the microlens aperture and that of the light emitting portion of the organic EL element are the same. Accordingly, the aforementioned problem can be solved by making the area of the microlens aperture larger than that of the light emitting portion of the organic EL element. However, when the area of the microlens aperture is made larger, there is a problem in that a distance between organic EL elements becomes larger, i.e. a pixel pitch increases, and unexposed portions are formed on an object to be exposed, thus making the organic EL elements impossible to function sufficiently as an exposure device.
In view of the aforementioned facts, an object of the present invention is to provide an exposure device capable of obtaining high availability of the emitted light, reducing optical crosstalk, and forming an image at high resolution.
In order to accomplish the aforementioned objects, a first exposure device is an exposure device comprising: a transparent substrate; rows which are formed on the transparent substrate, the rows including electric field light emitting elements arranged in a main-scanning direction and separated from one another at a predetermined spacing, the rows being arranged in a sub-scanning direction, and the electric field light emitting elements each including a light emitting portion; and microlenses, each one of which is formed on the transparent substrate so as to correspond to one of the electric field light emitting elements and focuses light emitted from the light emitting portion of the one electric field light emitting element for exposing an object to be exposed, wherein the one microlens has an aperture which is larger than an array pitch of the one corresponding electric field light emitting element, and the electric field light emitting elements are arranged such that a portion corresponding to a gap between portions exposed by the light emitting portions of one of the rows can be exposed by one of the light emitting portions of an adjacent one of the rows.
The first exposures device is an exposure device comprising: a transparent substrate; rows which are formed on the transparent substrate, the rows including electric field light emitting elements arranged in a main-scanning direction and separated from one another at a predetermined spacing, the rows being arranged in a sub-scanning direction, and the electric field light emitting elements each including a light emitting portion; and microlenses, each one of which is formed on the transparent substrate so as to correspond to one of the electric field light emitting elements and focuses light emitted from the light emitting portion of the one electric field light emitting element for exposing an object to be exposed.
In this exposure device, the aperture of the microlens is made larger than the array pitch of the electric field light emitting element corresponding to the microlens, whereby high availability of the emitted light can be obtained, and optical crosstalk can be inhibited. Further, the electric field light emitting elements are arranged so that a portion corresponding to a gap of the exposed portion exposed by the light emitting portion in one of the neighboring rows of the electric field light emitting elements can be exposed by the exposed portion of the light emitting portion in the other, whereby, even when a distance between respective electric field light emitting elements located on the exposure device becomes larger, a portion which is exposed by the light emitting portion (unexposed portion) of one of the neighboring rows can be exposed by the light emitting portion of the other, and the unexposed portions are not formed on the object to be exposed. Accordingly, an image can be exposed at high resolution.
In the first exposure device, image resolution in the main-scanning direction can be controlled by an array pitch of the electric light emitting element in the main-scanning direction, while image resolution in the sub-scanning direction can be controlled by an amount in which the exposure device and the object to be exposed relatively move in the sub-scanning direction (sub-scanning control amount). Therefore, the light emitting portions of the electric field light emitting elements are formed so as to have a predetermined dimension either in the main-scanning direction or the sub-scanning direction. And n rows of elements (n is an integer of 2 or more) are disposed in the sub-scanning direction, and the plurality of the electric field light emitting elements are arranged so that a main-scanning direction array pitch p between the light emitting portion of one of the neighboring rows of elements and the light emitting portion of the other satisfies a relationship of p=px/n, wherein px represents an array pitch of each of the rows of the electric field light emitting elements, whereby the configuration of the light emitting portion of the electric field light emitting element is not specifically limited, so it can be formed in an arbitrary shape such as circular, ellipse, or rectangular.
When a circular microlens is used, if the microlens is formed so that an aperture diameter D of the microlens satisfies a relationship of Dxe2x89xa6px, and Dxe2x89xa6(py2+p2)1/2, wherein py represents an array pitch of each row of elements in the sub-scanning direction, the center of the light emitting element and the center of the microlens are aligned, whereby each microlens can be disposed so as to correspond to each electric field light emitting element without overlapping one another.
Moreover, in the first exposure device, the aperture diameter D of a microlens is n times (n is an integer of 2 or more) of the array pitch p of the electric field light emitting element corresponding to the microlens, n rows of elements are disposed in the sub-scanning direction, and the electric field light emitting elements can be arranged so that a light emitting portion in one of the neighboring rows of elements and a light emitting portion in the other are shifted from each other in the main-scanning direction by the array pitch p.
In the exposure device in this state, the aperture diameter D of the microlens is n times the array pitch p of the corresponding electric field light emitting element, n rows of elements are disposed in the sub-scanning direction, and the electric field light emitting elements are arranged so that the light emitting portion in one of the neighboring rows of elements and the light emitting portion in the other are shifted from each other in the main-scanning direction by the array pitch p. In order to arrange a microlens having an aperture diameter D that is n times the array pitch p of the electric field light emitting element corresponding thereto, a distance that is (nxe2x88x921) times the array pitch p of the corresponding electric field light emitting element becomes necessary in the main-scanning direction and the sub-scanning direction, respectively. However, as described above, in this exposure device, the electric field light emitting elements are arranged so that a light emitting portion in one of the neighboring rows of elements and a light emitting portion in the other are shifted from each other by an array pitch p in the main-scanning direction, and n rows of elements are disposed in the sub-scanning direction. Accordingly, the object to be exposed can be exposed by the n rows of the elements without forming a gap between the rows, whereby unexposed portions are prevented from being formed on the object to be exposed, and image can be exposed onto the object to be exposed at high resolution.
A second exposure device of the present invention is an exposure device comprising: a transparent substrate; rows which are formed on the transparent substrate, the rows including electric field light emitting elements arranged in a main-scanning direction and separated from one another at a predetermined spacing, the rows being arranged in a sub-scanning direction, the electric field light emitting elements each including a light emitting portion, and the electric field light emitting elements being arranged so as to form a plurality of sets, each set including electric field light emitting elements that have mutually different light emitting wavelengths arranged in one of the main-scanning direction and the sub-scanning direction; and microlenses each one of which is formed on the transparent substrate so as to correspond to one of the sets of electric field light emitting elements, and focuses light emitted from the light emitting portions of the one set for exposing an object to be exposed, wherein the one microlens has an aperture which is larger than an array pitch of each of the electric field light emitting elements forming the one set of electric field light emitting elements, and the electric field light emitting elements are arranged so that a portion corresponding to a gap between portions exposed by light emitting portions of one light emitting wavelength in one of the rows can be exposed by one of light emitting portions, of the one light emitting wavelength in an adjacent one of the rows.
The second exposure device is an exposure device comprising: a transparent substrate; rows which are formed on the transparent substrate, the rows including electric field light emitting elements arranged in a main-scanning direction and separated from one another at a predetermined spacing, the rows being arranged in a sub-scanning direction, the electric field light emitting elements each including a light emitting portion, and the electric field light emitting elements being arranged so as to form a plurality of sets, each set including electric field light emitting elements that have mutually different light emitting wavelengths arranged in one of the main-scanning direction and the sub-scanning direction; and microlenses each one of which is formed on the transparent substrate so as to correspond to one of the sets of electric field light emitting elements, and focuses light emitted from the light emitting portions of the one set for exposing an object to be exposed.
In this exposure device, the electric field light emitting elements having different light emitting wavelengths are arranged so as to form a plurality of sets of the electric field light emitting elements which are arranged both in the main-scanning direction and the sub-scanning direction, whereby one microlens can be allocated to each of the electric field light emitting elements for forming a set thereof. The microlens aperture is made larger than the array pitch of each of the electric field light emitting elements for forming a set of the electric field light emitting elements corresponding thereto, whereby availability of the emitted light amount increases, and optical crosstalk can be reduced. Further, the electric field light emitting elements are arranged so that a portion corresponding to a gap of each portion exposed by the light emitting portions of the same light emitting wavelength in one of the neighboring rows containing the electric field light emitting elements of the same light emitting wavelength can be exposed by the light emitting portions of the same light emitting wavelength in the other. Accordingly, even when a distance between the electric field light emitting elements becomes larger in accordance with the microlens aperture, an unexposed portion by the light emitting portions in one of the neighboring rows can be exposed by the light emitting portion in the other, whereby it becomes possible to prevent unexposed portions from being formed on the object to be exposed, and image can be exposed onto the object to be exposed at high resolution.
Moreover, in the exposure device described above, the microlens used a convex lens formed at the light emitting side of the transparent substrate, a distribution refracting lens inside the transparent substrate, and a combination lens of the convex lens and the distribution refracting lens can be used.
In this exposure device, it is preferable that an organic electric field light emitting element is used as an electric field light emitting element.
If a gap is formed between the neighboring microlenses, a portion of the light of the emitted light that has been forwarded to the gap is not only unavailable for the exposure but also is converted to stray light, thus leading to the deterioration of image quality. For this reason, in the aforementioned exposure device, it is preferable that the neighboring microlenses are formed by being kept in close contact with each other. Further, it is more preferable that the aperture of one of the neighboring microlenses and that of the other are partially overlapped. For example, when a microlens aperture corresponding to one light emitting element is formed so as to correspond each of sides or borders of the microlens to a vertical bisector of the line connecting the light emitting element and the light emitting element neighboring thereto, the connecting portion can be linearly kept in close contact with each other. Thus, the neighboring microlenses are kept in close contact with one another, whereby almost the entire amount of the emitted light from the electric field light emitting elements can be used for the exposure, and availability of the emitted light can be substantially maximal.